The part of her answer I’m guessing you’re referring to is this:
It doesn't matter if your work has been on any of these sites. You just need to tell me about it in the query. The reason you need to tell me is that if we work together to sell your book, I have to tell the editor.
You can indeed interpret that first sentence as “posting on these sites doesn’t matter,” so if that’s the case, I totally see where you’re coming from. I’d be happy if that were the case!
I’m not certain, but I personally think what she means there is “if your work has been posted on any of these sites, don’t let that stop you from querying; just make sure you mention it up front.”
However, the part of her answer from which I’m pulling the conclusion in my original post is the following text:
And we must make sure any publishing contract reflects the fact that this work has been previously published.
Previously published is NOT a deal breaker; we just need to adjust the contract language.
I’m interpreting “previously published” to mean a piece of content that has been published before, AKA has used the “first rights” already.
If you read other sources about trying to get “previously published” works published, you’ll find that people saying that it’s more difficult to get said work published vs. something that hasn’t been published anywhere; there are agents, publishers, and publications that won’t even consider previously published work.
That said, the degree of added difficulty is uncertain, and querying a previously published work doesn’t guarantee rejection, so it’s up to you to decide how much that matters to you.